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						<h1 id="firstHeading" class="firstHeading" lang="en"><span dir="auto">JPEG</span></h1>
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								<div id="siteSub">From PanoTools.org Wiki</div>
								
												
				<div id="mw-content-text" lang="en" dir="ltr" class="mw-content-ltr"><p><br />
<b>JPEG</b> is an image file format<a class="external" href="http://wiki.panotools.org/Image_format">[*]</a> for storing and distributing images, particularly photographs.
For a detailed technical overview, please refer to the WikiPedia JPEG page<a class="external" href="http://www.wikipedia.org/wiki/JPEG">[*]</a>.
</p><p><b>JPEG</b> files typically have a <i>.jpg</i> file extension.
If you can't see file extensions, you may want to enable windows file extensions<a class="external" href="http://wiki.panotools.org/Enable_windows_file_extensions">[*]</a>
as you will have great difficulty editing and manipulating image files otherwise.
</p><p>Digital cameras typically default to saving photographs in <b>JPEG</b> format as it provides a
good compromise between quality and filesize for most uses.
<b>JPEG</b> is also a good format for delivering photographic images over the web or in email.
</p>
<div id="toc" class="toc"><div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="JPEG.html#Compression_issues"><span class="tocnumber">1</span> <span class="toctext">Compression issues</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="JPEG.html#EXIF_issues"><span class="tocnumber">2</span> <span class="toctext">EXIF issues</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="JPEG.html#Color_downsampling_issues"><span class="tocnumber">3</span> <span class="toctext">Color downsampling issues</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="JPEG.html#Other_JPEG_limitations"><span class="tocnumber">4</span> <span class="toctext">Other JPEG limitations</span></a></li>
</ul>
</div>

<h3><span class="mw-headline" id="Compression_issues">Compression issues</span></h3>
<p><b>JPEG</b> is a <i>lossy</i> compressed file format, this means that a lot of information that is imperceptable to the human eye is discarded - Converting to another file format will <i>not</i> restore this missing data.  
</p><p>Unfortunately this degradation can become perceptable if an image is later manipulated, so if you intend to produce high-quality work you might want to switch your camera to take photos in lossless <a href="TIFF.html" title="TIFF">TIFF</a>, <a href="RAW.html" title="RAW">RAW</a> or DNG<a class="external" href="http://wiki.panotools.org/index.php?title=DNG&amp;action=edit&amp;redlink=1">[*]</a> format instead.
</p><p>There are a small number of <b>JPEG</b> manipulations that can be performed losslessly, such as cropping, rotation (at 90 degree angles), flipping and removal of <a href="CCD.html" title="CCD">CCD</a> artefacts such as <i>bad pixels</i> (see <a rel="nofollow" class="external text" href="http://www.zero-based.org/software/jpegpixi/">Jpegpixi</a>).
</p>
<h3><span class="mw-headline" id="EXIF_issues">EXIF issues</span></h3>
<p>Modern cameras save a lot of information about a photograph (time, lens and exposure data) within the <b>JPEG</b> file as <a href="EXIF.html" title="EXIF">EXIF</a> data.  If you are having trouble, one of these causes may be to blame:
</p>
<ul>
<li> Rotating a photo may simply flip an <a href="EXIF.html" title="EXIF">EXIF</a> tag from <a href="Landscape.html" title="Landscape">Landscape</a> to <a href="Portrait.html" title="Portrait">Portrait</a> without changing the image itself.  The resulting image may or may not appear rotated depending on the viewing software.
</li>
</ul>
<ul>
<li> Rotating a photo may rotate the image without changing any <a href="EXIF.html" title="EXIF">EXIF</a> data to suit, this may cause problems when a GUI tool reads the <a href="Field_of_View.html" title="Field of View">Field of View</a> from the file.  To avoid this, use a tool like photomolo<a class="external" href="http://wiki.panotools.org/index.php?title=Photomolo&amp;action=edit&amp;redlink=1">[*]</a> to do lossless rotation and let it reset the <a href="EXIF.html" title="EXIF">EXIF</a> tags appropriately.
</li>
</ul>
<ul>
<li> Opening and saving a photo may discard all the <a href="EXIF.html" title="EXIF">EXIF</a> data, switch to another image editor.
</li>
</ul>
<h3><span class="mw-headline" id="Color_downsampling_issues">Color downsampling issues</span></h3>
<p><b>JPEG</b> isn't an RGB file format where each of three red, green and blue channels are saved alongside each other.  A <b>JPEG</b> image is typically a monochrome image with two lower resolution color channels.
</p><p>This means that applications where color integrity is important like correcting <a href="Chromatic_aberration.html" title="Chromatic aberration">chromatic aberration</a> are not suitable uses for <b>JPEG</b> data.
</p>
<h3><span class="mw-headline" id="Other_JPEG_limitations">Other JPEG limitations</span></h3>
<p><b>JPEG</b> doesn't support multiple layers, <a href="Alpha_channel.html" title="Alpha channel">alpha channels</a> or high <a href="Dynamic_range.html" title="Dynamic range">dynamic range</a> which means that it isn't much use for <i>work in progress</i> either.  When working with such data, lossless file formats are preferable such as <a href="PNG.html" title="PNG">PNG</a>, <a href="TIFF.html" title="TIFF">TIFF</a>, <a href="PSD.html" title="PSD">PSD</a> or XCF<a class="external" href="http://wiki.panotools.org/index.php?title=XCF&amp;action=edit&amp;redlink=1">[*]</a>.
</p>



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